The unit dissipation is cumulative the more you drink the longer it takes to get the next unit out of your system. (If you had just a half and killed a kid would you be asking yourself if you could have avoided the accident if you were sober? I know I would so rather than second guess the dissipation levels I have 0 units before driving.)
(Mobile licencing! Take the wheels off get the licence and badge to go over the door and you then put the wheels on - problem solved!

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